Hard-core advocates for and against the Iraq war are losing leverage as John McCain and Barack Obama, having virtually secured their nominations, appeal to centrist voters who will decide the fall presidential election.

McCain recently suggested 2013 as a possible end to U.S. involvement in Iraq. Many saw it as a switch from his earlier denouncements of timelines, although McCain insisted it was not.

Obama continues to tell audiences he will remove U.S. combat troops within 16 months of taking office. Sometimes he seems to shorten it to 11 months, saying, "I will bring this war to an end in 2009."

But his top aides are careful to note several caveats he has embraced, even if he rarely emphasizes them. They include leaving an unspecified number of "residual forces" in Iraq and promising to listen to military advisers before making final decisions.

"Our best estimate is that we can get the bulk of our combat brigades out within 16 months," Susan Rice, a top military adviser to Obama, said in an interview. "It's a timeline, it's a goal."

Economic worries, coupled with an Iraq that is less violent than it was a year ago, have pushed the five-year-old war from the top of voters' concerns and off many front pages. But it will get plenty of attention this week, as top Iraqi commander David H. Petraeus testifies before Congress on Thursday, and the candidates hit military themes for Memorial Day.

Many nonpartisan military experts predict that Obama, if elected president, will move more cautiously to disengage from Iraq because a 12-month or 16-month pullout might trigger sharp spikes in violence and political turmoil there.

"I don't know anybody working on this at a senior level who thinks that is plausible," said Brookings Institution military scholar Michael O'Hanlon, who sees important gains from the Bush administration's 2007 "surge" in U.S. troops sent to Iraq.

Even some of Obama's strongest supporters think he is likely, if elected, to take a more deliberate approach to turning Iraq's security over to Iraqi forces.

Obama is "wise not to get too far down in the weeds" of promising exactly how and when he would withdraw U.S. forces, said Matt Bennett, vice president of Third Way, a policy group with centrist-Democratic leanings. "You don't want to tie your hands," he said.

A slower disengagement process would subject Obama to "extraordinary pressure" from infuriated anti-war groups, Bennett said, noting they have helped him outmaneuver Hillary Rodham Clinton in the primary season.

"The Code Pink people will go into full overdrive," he said, referring to one such group. "But I think Obama will have a lot of latitude" because he would enter the White House with a powerful mandate as a "transformational president."

Whatever the pace, however, Obama would have to withdraw substantial numbers of U.S. forces from Iraq because the Army is nearing a breaking point, Bennett said. Meanwhile, he said, more troops are badly needed in Afghanistan, which Obama calls a must-win war against al-Qaida and its allies.

On the Republican side, McCain caught some supporters and opponents by surprise last week when he stated for the first time that he believes the Iraq war can be won in less than five years.

"By January 2013, America has welcomed home most of the servicemen and women who have sacrificed terribly," he said in an Ohio speech in which he envisioned happy endings to his first term as president. "The Iraq War has been won." Continued...